Appendix C. Collected ABNF (收集的 ABNF)

ETag = entity-tag

HTTP-date = <HTTP-date, 见 [RFC7231], 第 7.1.1.1 节>

If-Match = "*" / 1#entity-tag
If-Modified-Since = HTTP-date
If-None-Match = "*" / 1#entity-tag
If-Unmodified-Since = HTTP-date

Last-Modified = HTTP-date

entity-tag = [ weak ] opaque-tag
etagc = %x21 / %x23-7E / obs-text
   ; 除双引号外的 VCHAR, 加上 obs-text

obs-text = <obs-text, 见 [RFC7230], 第 3.2.6 节>
opaque-tag = DQUOTE *etagc DQUOTE
weak = %x57.2F ; "W/", 区分大小写